Python hasattr()

Python’s built-in hasattr(object, string) function takes an object and a string as an input. It returns True if one of the object‘s attributes has the name given by the string. Otherwise, it returns False.

Usage

Learn by example! Here’s an example on how to use the hasattr() built-in function.

# Define class with one attribute
class Car:
    def __init__(self, brand):
        self.brand = brand


# Create object
porsche = Car('porsche')

# Check if porsche has attributes
print('Porsche has attribute "brand": ', hasattr(porsche, 'brand'))
print('Porsche has attribute "color": ', hasattr(porsche, 'color'))

The output of this code snippet is:

Porsche has attribute "brand":  True
Porsche has attribute "color":  False

It has the attribute “brand” but not the attribute “color”.

Video hasattr()

Syntax hasattr()

The hasattr() object has the following syntax:

Syntax: 
hasattr(object, attribute)         # Does the object have this attribute?

Return value from hasattr()

The hasattr(object, attribute) method returns True, if the object has the attribute and False otherwise.

Interactive Shell Exercise: Understanding hasattr()

Consider the following interactive code:

Exercise: Fix the code so that both results of hasattr() return True!

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Applications hasattr()

• You can use hasattr() to avoid accessing errors when trying to access an attribute of a dynamic object.
• You can use hasattr() in a ternary operator to conditionally assign a value to a variable such as in: age = object.age if hasattr(object, 'age') else 0
• However, be careful when using hasattr() as it always return False, no matter the error message. Thus, it may overshadow an error different to the error that appears if the attribute doesn’t exist. So, the attribute may indeed exist but if trying to access it causes an error, the result will be False.

Related Functions

• The getattr() function returns the value of an attribute.
• The setattr() function changes the value of an attribute.
• The hasattr() function checks if an attribute exists.
• The delattr() function deletes an existing attribute.

Summary

Python’s built-in hasattr(object, string) function takes an object and a string as an input.

• It returns True if one of the object‘s attributes has the name given by string.
• It returns False otherwise if one of the object‘s attributes doesn’t have the name given by string.

>>> hasattr('hello', 'count')
True
>>> hasattr('hello', 'xxx')
False

Note that hasattr() also returns True if the string is the name of a method rather than an attribute.

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While working as a researcher in distributed systems, Dr. Christian Mayer found his love for teaching computer science students.

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